Electric heating unit



JulY'16, 1957 w. H. JENKINS ETAL 2,799,765

ELECTRIC HEATING UNIT Filed Jan. 31, 1955 Ihwentors //s 70 JEN/(INS nxva FEEDER/CK SC/{EASY M 6 atto rneg nit g ELECTRIC HEATING UNIT Application January 31, 1955, Serial No. 485,159

12 Claims. (Cl. 21937) The present invention relates to electric heating units particularly suitable for use as the surface units of electric ranges, hot plates, and other appliances of a similar character.

It has been common practice to provide open type heating units embodying heating wire coils embedded in spiral grooves formed in the top surface of a suitable ref-ractory disc. The exposed heating coils of such units are, however, subject to become short-circuited due to spilling of food, as well as oxidation and deterioration from the same cause. Moreover, such coils are frequently damaged by attempts to clean them.

To over-come the faults inherent in the open type units it has been proposed to employ two suitable refractory discs placed together with the heating coil enclosed therebetween. Such a construction avoids many of the disadvantages of units of the open type, but requires great care in the choice of discs employed and their manner of assembly if a satisfactory unit is to result. The most common faults of such: units are that the top discs are unable to withstand the thermal shocks to which they are repeatedly exposed; Moreover, such discs may be readily soiled, diflicult to clean, and subject to warping and cracking; and unless they are made of a material which is relatively transparent to infrared rays to enable them to readily direct such rays upwardly towards their cooking surface, they are inefficient. Also unlessthe lower disc is com-posed of a material that is an efiicient thermal insulator and, because of its non-absorbent character, remains so in use, excessive heat loss eventually occurs through the lower side of the; unit. Moreover, if the design is not correct grease drippings and the like will seep between the discs and into association with the heating element to such an extent as to short-circuit series of convolutions or sections of the heating elements and thus cause their premature failure.

According to the invention a heating unit of the foregoing general type is free of the faults above outlined is provided. Such unit comprises a relatively thin shallow skirted ware supporting disc composed of a high silica glass composition similar to those disclosed in Patents No. 2,106,744 and No. 2,221,709 and which is a near-transparent dense, non-porous material capable of withstanding extreme thermal shock and relatively transparent to infrared rays. Desirably, although not necessarily, the interior surface of the bottom of such disc which is spirally grooved to receive suitably formed heating elements of convention al form, may be coated with a fired-on frit to give the disc an opalescent appearance. Such a coating may be made by spraying the grooved dis-c surface with a slurry of powdered glass in a solution of methanol and butanol and firing the same after drying in air. Alternatively the disc may be manufactured in opalescent rather than transparent form.

The heating elements are held supported in the grooves of the first disc by means of a relatively thick disc of a diameter to closely fit within the confines of the skirt States Patent of the first disc composed of fluid impervious cellular electrical and thermal insulating foam silica. The respective discs are held rigidly with respect to one another and with the heating element sandwiched therebetween by means of a sheet metal shell of stainless steel or other suitable material provided with ventilating apertures arranged in a row parallel to and adjacent or near the peripheral line of juncture of the two discs. In addition the shell bottom is provided with an annular trough near the peripheral region of the relatively thick disc surface opposite that engaging the first disc. Such annular trough has a number of bottom passages for the quick drainage of any material therefrom that may find its way thereto.

A preferred embodiment of the invention is illustrated in the accompanying drawing wherein Fig. 1 is a sectional elevation of the unit taken on line 11 of Fig. 2, and wherein Fig. 2 is a bottom plan view of the unit.

Referring; to the drawing in detail the unit embodies a relatively thin disc 11 having a shallow skirt 12 the free edge of which is provided with a peripheral bead 13. The under surface of disc 11 is provided with grooves of conventional spiral form in which are arranged helical-type coil heating elements 16 and 17. Lead wires 18 and 19 from the element 16 are projected through suitable passages in a relatively thick heating element supporting refractory disc unit or member 20 and are connected with terminals 2i and 22 mounted on a suitable terminal support 35. Similar lead wires also extend from the element 17 through passages of the disc 20 and connect with the terminals 22 and 23' respectively.

The discs 11 and 20 and thesupport 35 are arranged with. their opposing surfaces in engagement with one another, with the upper portion of the vertical wall surface 15 of disc 20 slightly overlapped by the vertical inner s urface 14 of the disc skirt 12. Also, the discs 11 and 20 and the support 35 are at least in part confined within a cup-shaped sheet metal shell having a sidewall 25' and an adjoining annular bottom wall whose peripheral regionis in the form of a trough 26 provided with a series of drain apertures 37. The discs 11 and 20 are clamped between an intermediate annular region 28 of the shell bottom and the flared out top edge 30 of the shell wall 25, the free edge of which is folded or spun over the edge of bead 13. The terminal support 35 bridges a central passage 31 therethrough in the region occupied by terminals 21, 22 and 23, and is attached to the shell by means of suitable bolts 33 and 34.

As will be understood, with such a structure, because of the close fit of the wall portion 30 of the shell over the bead 13 and because of the overhang of the skirt 12 below the meeting surfaces of discs 11 and 20, entry of highly fluid grease into the interior of the shell is substantially wholly prevented. Such grease, however, that finds its way between the wall edge 30 and bead 13 is ordinarily quickly dissipated or consumed before it can reach the lower region of the vertical line of juncture of surfaces 14 and 15, because of the freedom of air circulation made possible by the provision of the apertures 27 in the shell. On those infrequent occasions that a large volume of spillage on the surface plate 11 may occur and that may result in abnormal seepage of grease between the disc 11 and the shell edge 30 such grease is free to flow down the inner surface of wall 25 into the trough 26 and to issue from the drainage passage 37. Moreover, any globules of fluid that might otherwise tend to accumulate and enter the vertical line of juncture of such discs are in a sense siphoned away therefrom when the volume of fluid entering the shell is sufficient to flow down its inner wall.

From the foregoing it will be appreciated that applicants have provided a form of heating unit wherein the heating coils are held between two refractory discs having lines of juncture that effectively hinder the entrance of grease therebetween; and that are rigidly held within a shell that facilitates the ready dissipation and/ or drainage therefrom of any grease that may find its way therein in a novel fashion as defined in the appended claims.

What is claimed is:

1. In an electric heating unit, a relatively thin circular skirted disc with the free edge of the skirt externally beaded, an electric heating element occupying grooves in the inner surface of said disc; a relatively thick disc of circular outline, composed of heat resistant gas impervious thermal insulating material, whose top surface is arranged against the grooved side of said first disc within the confines of the skirt thereof; a metal shell having an annular bottom covering the annular perpiheral portion of the bottom surface area of said second disc and having an adjoining wall surrounding said second disc with a bordering flange portion of such wall projecting inwardly over the beaded edge of said first disc, said shell wall having apertures therethrough arranged in a row parallel to and slightly below the bottom of the edge of said first disc exposing the region of the line of juncture of said discs to atmosphere.

2. An electric heating unit such as defined by claim 1 wherein the region of the shell wall containing the row of apertures is flared outwardly from the perimeter of the second disc.

3. An electric heating unit such as defined by claim 1 wherein the outer region of the shell bottom is in the form of an annular trough and has drain holes therein.

4. An electric heating unit such as defined by claim 1 which includes a set of terminals and a support therefor comprising a bridge of insulating material extending across the passage afforded by said annular shell bottom.

5. An electric heating unit such as defined by claim 1 wherein the second disc is provided with heating element terminal lead wire passages between central and lateral regions of the heating element respectively and said terminals.

6. In an electric heating unit, a relatively thin disc having a beaded skirt of circular outline and being composed of a heat resistant vitreous material which is relatively transparent to infrared rays; a relatively thick disc of circular outline, composed of a heat resistant gas impervious thermal insulating material, adjacent the inner side of said first disc within the confines of the skirt thereof; an electric heating element occupying a groove Cir in one of said discs closed by the adjacent disc, a metal shell having an annular bottom covering a portion of the surface area of said second disc having a bordering flange projecting inwardly over the beaded edge of said first disc and containing a row of ventilating apertures adjacent and parallel to such flange, whereby the discs and heating element are closely confined therein while the outer border region of the region of the line of juncture of said discs remains exposed to atmosphere.

7. In an electric heating unit, relatively thin and relatively thick circular discs of refractory material having sandwiched therebetween an electric heating element occupying a groove in one of said discs, a shell for maintaining said discs in tightly bound relation having a bottom portion engaged by one of said discs and provided with a wall portion surrounding said discs with the free edge of such wall portion having apertures therethrough arranged in a row parallel to and near the bordering line of juncture of said discs.

8. In an electric heating unit such as defined by claim 7 wherein the wall bordering bottom portion of such shell is in the form of an annular trough provided with drainage apertures.

9. An electric heating unit such as defined by claim 7 wherein the diameter of the thin disc exceeds that of the thick disc and wherein the wall of the shell in the region adjoining the region containing the row of apertures is flared outwardly away from the thick disc to a diameter to receive the thin disc.

10. An electric heating unit such as defined by claim 7 wherein the thin disc is composed of a dense refractory ceramic material and the thick disc is composed of a gas impervious cellular refractory material.

11. An electric heating unit such as defined by claim 9 wherein the thin disc is provided with a shallow skirt that overhangs the adjacent bordering edge of the relatively thick disc.

12. An electric heating unit such as defined by claim 4 wherein the support for the terminals is in part sandwiched between the shell and the relatively thick disc.

References Cited in the file of this patent UNITED STATES PATENTS 1,260,252 Apfel Mar. 19, 1918 2,179,934 Jones Nov. 14, 1939 2,486,862 Meyer Nov. 1, 1949 2,518,015 Jefirey Aug. 8, 1950 2,601,011 Wilcox June 17, 1952 

